Is BLDC motor star connected or delta connected?

BLDC motors are usually in small capacity ratings, and it is universally adopted principle across word to use star connection (either internal or external) in small HP motors. Anyway, Star or delta connection matters only in case of motor with 6 leads and operating with star-delta starter, which is never a case with BLDC motor.

Star/Delta connection matters only when there are six leads and starter is star-delta starter, which is not a case for BLDC motor.

As to know where the three leads motor is star connected or delta can be known from motor RTC, in which it is mandatory to mention type of connection as per Indian Standard. In case it is not mentioned, then the other method is to measure the resistance between leads and compare it with phase resistance (which is a must to mention in RTC as per IS as well as IEC). If the resistance between leads is more than declared value of phase resistance, it is delta connection. If it is less, it is star connection.

Star or delta connection has nothing to do with supply voltage. All medium and large voltage motors operating at 1.1 kv, 3.3 kv, 6.6 kv and more are ALL designed for star connection. And all low voltage motors (690v or less) are designed for delta connection except small HP ratings. And yes, if there are six leads, then you can operate motor in both star and delta connection, but at different voltage. E.g. 415 V motor in delta connection can be used with star connection and 690 v (applying the same 415 V in star connection lowers motor rated capacity and it may get burnt due to overload) and 415 V motor in star connection can be used in delta with 230V.

With the characteristic of a BLDC in mind (Unidirectional current between any two phases, third phase remains idol), it can constructively be concluded that BLDC motors are ALWAYS star connected, because only in star connection, if you apply voltage source between any two leads, the current flows between two phases connected in series, leaving the third phase unenergized. In case of delta connection, even if any two leads are connected to voltage source, all the three phase are energized with various magnitude because if parallel connection of phases.